I had the same problem. If you have access to the older issues, specifically Issue 175 (Summer/Fall 2016, pg. 35), I wrote up my experience. Succinctly, I had a hole in the passenger exhaust manifold which, I think, was original and, I also think, machined to accept a stovepipe which led up to the (engine heated) automatic choke. Mine is a '66 and carbureted but now has a different choke mechanism; I don't know if yours is similarly equipped.
The hole is on the inner side of the manifold and goes up through the exhaust pipe mounting flange into the heat riser mechanism. I started a 5/16-18 regular tap and finished with a 5/16-18 bottoming tap and made about 6 complete threads. Both Noise and exhaust smell significantly reduced.
Good luck.